Liquid crystal display device

ABSTRACT

A liquid crystal display device having superior moving-image display characteristics are provided. In the liquid crystal display device, the timing of application of grayscale voltage to liquid crystal cells at the top end of its screen with respect to the timing of application of grayscale voltage to liquid crystal cells in the center of the screen and the timing of application of grayscale voltage to liquid crystal cells at the bottom end of the screen with respect to the timing of application of grayscale voltage to the liquid crystal cells in the center of the screen are made approximately coincident with each other or are deviated from each other by approximately one scanning-line selection period, and a liquid crystal panel is illuminated by a backlight which is intermittently lit in synchronism with vertical synchronizing signals.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display.

[0003] 2. Background Art

[0004] A related art liquid crystal display device will be describedbelow with reference to FIGS. 1, 3 and 4. FIG. 1 is a block diagram of ageneral liquid crystal display device. FIG. 3 shows the timing of a gateselecting signal which is generated from a general scanning drivercircuit and is applied to a TFT liquid crystal display. FIG. 4 shows thetransmissivity of liquid crystal cell, the luminance wave form of abacklight and a variation in the luminance of a liquid crystal panel inthe case of applying grayscale voltage at the timing shown in FIG. 3with causing the backlight to light intermittently in synchronism withvertical synchronizing signal.

[0005] In FIG. 1 101 denotes a data bus over which to transmit displaydata and a synchronizing signal which are inputte from an externaldevice, 110 denotes a timing control circuit which generates varioustiming signals for a liquid crystal driver circuit, 111 denotes a databus over which to transmit display data and a synchronizing signal whichare generated by the timing control circuit 110, and 112 denotes asignal bus over which to transmit a synchronizing signal generated bythe timing controll circuit 111. 113 denotes a signal driver circuitwhich generates grayscale voltages according to the display datatransmitted over the data bus 111. 114 denotes the scanning drivercircuit which sequentially selects a line to which to apply thegrayscale voltage generated by signal driver circuit 113. 115 denotes apower source circuit, and 116 denotes a liquid crystal panel. 117denotes drain line buses over which to transmit to the liquid crystalpanel 116 the grayscale voltages generated by the signal driver circuit113. 118 denotes gate line buses over which to transmit scanningvoltages generated by the scanning driver circuit 114 to the liquidcrystal panel 116. 119 denotes a power source bus over which to transmita power source voltage to the signal driver circuit 113, and 120 denotesa power source bus over which to transmit a power source voltage to thescanning driver circuit 114.

[0006] The operation of the liquid crystal display device shown in. FIG.1 wi 11 be described below in detail. Display data and a synchronizingsignal which are inputted through the bus 101 from an external deviceare converted through the timing control device 110 into display dataand a synchronizing signal which operate the signal driver circuit 113and the scanning driver circuit 114, and the obtained display data andsynchronizing signal are transmitted to the data bus 111 and the signalbus 112. The signal driver circuit 113 converts the display transmittedover the data bus 111 into a corresponding grayscale voltage, andoutputs the corresponding grayscale voltage to the drain line buses 117.The grayscale voltage transmitted over the drain line buses 117 isapplied to the liquid crystal panel 116, whereby the display data can beseen by the human eye in the form of a display luminance correspondingto the display data.

[0007] This operation will be described below with reference to FIGS. 3and 4 which show the timing of scanning-line selection, a transmissivity304 of liquid crystal cells lying at the top end of the screen, atransmissivity 305 of liquid crystal cells lying in the center of thescreen, a transmissivity 306 of liquid crystal cell lying at the bottomend of the screen, a luminance 307 of the backlight which is driven tolight intermittently in synchronism with the vertical synchronizingsignal, a luminance variation 308 of the liquid crystal panel at the topend of the screen during a period of time in which the transmissivity ofthe liquid crystal cells lying at the top end of the screen is in itstransient state before reaching its steady state, when a display imagesignal changes from black to white, a luminance variation 309 of theliquid crystal panel in the center of the screen during a period of timein which the transmissivity of the liquid crystal cells lying in thecenter of the screen is in its transient state before reaching itssteady state, when the display image signal changes from black to white,a luminance variation 310 of the liquid crystal panel at the bottom endof the screen during a period of time in which the transmissivity of theliquid crystal cells lying at the bottom end of the screen is in itstransient state before reaching its steady state, when the display imagesignal changes from black to white.

[0008] In a general liquid crystal display device having pixels arrangedin M vertical columns and N horizontal rows, as shown in FIG. 3, wi thina vertical write period (frame period) 301 (16.7 mS in the case of ascreen display frequency of 60 Hz), the first scanning line is selectedand the image display signal in the first line is converted into acorresponding grayscale voltage, and this grayscale voltage is outputtedto the drain signal line buses to set the liquid crystal cells to thedesired transmissivity. Subsequently, scanning-line selection, theoutputting of grayscale voltage to the drain line buses, and the settingof the transmissivity of the liquid crystal cells are sequentiallyrepeated in the order of the second line, the third line and so on. Thesetting of the transmissivity of liquid crystal cells for one screen iscompleted with the setting of the transmissivity of the liquid crystalcells on the N-th line. The grayscale voltages which have been set forthe respective liquid crystal cells are held in the capacitances of therespective liquid crystal cells and in storage capacitances provided inthe respective liquid crystal cells, until the individual liquid crystalcells are subjected to the next setting cycle, i.e., scanning-lineselection, the outputting of grayscale voltage to the drain line busesand the setting of the transmissivity of the liquid crystal cells.

[0009]FIG. 4 shows the relationship among the transmissivities of theliquid crystal cells, the luminance of the backlight and the luminanceof the liquid crystal panel in the case where scanning-line selection isperformed at the timing shown in FIG. 3 and the backlight is driven tolight intermittent Iy in synchronism with the vertical synchronizingsignal.

[0010] In the case where the lighting start timing of the backlight isset so that the luminance variation of the liquid crystal panel in thecenter of the screen becomes most natural while a moving image is beingdisplayed on the TFT liquid crystal display, the luminance waveform ofthe backlight becomes as shown in FIG. 4.

[0011] In other words, assuming that the luminance response of thebacklight to a backlight blinking control signal is faster than theresponse of the transmissivity variation of the liquid crystal cells tothe application of grayscale voltage to the liquid crystal cells, when,after the application of grayscale voltage to the liquid crystal cellsin the center of the screen, a backlight lighting start signal isapplied to switch the backlight from off to on, for example in the casewhere display data is changed from black to white, the time required fora variation in the luminance of the liquid crystal panel becomesapparently faster than that required for a variation in transmissivityof the liquid crystal cells.

[0012] According to documents such as Examination of Moving ImageQuality of Hold Emission Type Display Using 8 Times Speed CRT (TechnicalReport of The Institute Of Electronics, Information and CommunicationEngineers, EID 96-4, pp. 19-26, June 1996) or Examination of ViewingMechanism During Display of Moving Image on Hold Type Display (TechnicalReport of The Institute of Image Information and Television Engineers,Vol. 122, No. 17, pp. 19-24, March 1998), it has been known that if amoving image is displayed on a TFT liquid crystal display, a degradationof image quality which is called a moving-image blur occurs owing to thefact that grayscale voltages are held in its liquid crystal cells forone frame period.

[0013] A CRT generally emits light for as short as ⅛ of one frame period(16.7 mS in the case of a screen display frequency of 60 Hz), andcontinues to display black for the remaining period. In this form ofemission, moving-image blur does not occur. For this reason, variousmethods of coping with moving-image blur by inserting periods in whichno image is displayed have been proposed with respect to TFT liquidcrystal displays.

[0014] A method of inserting a period in which no image is displayed, ascountermeasures against moving-image blur, is disclosed in JapanesePatent Laid-Open Nos. 109921/1999 and 293142/2000.

[0015] The intermittent lighting of the backlight in synchronism withthe vertical synchronizing signal 302 shown in FIG. 4 is in tended forsuch countermeasures against moving-image blur. As described above, thelighting start timing of the backlight is set so that the luminancevariation of the liquid crystal panel in the center of the screenbecomes most natural. Therefore, the luminance of the liquid crystalpanel gradually increases like the luminance 309 of the liquid crystalpanel during the period of time in which the transmissivity of theliquid crystal cells lying in the center of the screen is in thetransient state before reaching the steady state, when display data inthe center of the screen changes from black to white. Furthermore, theluminance variation of the liquid crystal panel becomes faster than theresponse of the transmissivity variation of the liquid crystal panel tothe application of grayscale voltage to the liquid crystal panel.Accordingly, it is possible to realize only the advantage of thecountermeasures against moving-image blur due to the insertion of apredetermined length of off period in the period of the backlight.

SUMMARY 0F THE INVENTION

[0016] However, at the top end of the screen, the transient responseperiod of back light extinction and the transient response period of thetransmissivity of the liquid crystal cells over lap each other, so thatwhile the luminance of the liquid crystal panel changes from black towhite as shown at 308 in FIG. 4 (308: the luminance of the liquidcrystal panel during a change from black to white at the top end of thescreen) , light of low luminance is emitted from the liquid crystalpanel. Within the write period 301, the next time at which the top endof the screen emits is the timing at which the backlight startslighting, and the luminance of the liquid crystal panel at that timevaries similarly the luminance of the backlight.

[0017] The present inventor has newly discovered that after light of lowluminance (an image of low contrast) has once been seen by the humaneye, light of high luminance (an image of high contrast) can be seen bythe human eye, and this phenomenon leads to the problem that while animage is moving, the contour of the image is seen double.

[0018] The present inventor has also discovered that at the bottom endof the screen, while an image is changing from black to white, theluminance of the liquid crystal panel does not gradually increase, sothat while a moving image is being displayed, the contour of the imageis seen double.

[0019] Furthermore, since the top and bottom ends of the screen differin the manner of luminance variation of the liquid crystal panel, thetop and bottom ends of the screen cannot be improved at the same timeunder conditions which optimize the state of displ ay of a moving imagein the center of the screen. Even if an are a in which the luminancevariation of the liquid crystal panel becomes most natural is moved fromthe center toward the top or bottom of the screen by deviating thelighting start timing of the backlight, it is impossible to improved thetop end and the bottom end of the screen, because the manner of theluminance variation of the liquid crystal panel is asymmetrical at thetop end and the bottom end of the screen.

[0020] When image display data changes from black to white in an areaexcept the top end, the center and the bottom end of the screen, theliquid crystal panel shows the following luminance variation.Scanning-line selection is sequentially performed to start at the firstline and complete at the N-th line, i.e., the application of grayscalevoltage to the liquid crystal cells are temporally sequentially delayed(deviated), so that the luminance of the liquid crystal panel graduallyvari es from the luminance 308 which occurs in the liquid crystal panelat the top end of the screen during a period of time in which thetransmissivity of the liquid crystal cells lying at the top end of thescreen is in its transient state before reaching its steady state, whendisplay data at the top end of the screen changes from black to white.Subsequently, the luminance of the liquid crystal panel reaches theluminance 309 of the liquid crystal panel in the center of the screen aswell as the luminance 310 of the liquid crystal panel at the bottom endof the screen.

[0021] Therefore, when a moving image is displayed in the center of thescreen, its contour is not seen double, but the contour becomes seengradually double toward the top or bottom end of the screen, and themanner in which the double contour is seen differs between the top andbottom ends of the screen. In the above-described method, the timing ofapplication of grayscale voltage to the liquid crystal cells at the topend of the screen with respect to the timing of application of grayscalevoltage to the liquid crystal cells in the center of the screen and thetiming of application of grayscale voltage to the liquid crystal cellsat the bottom end of the screen with respect to the timing ofapplication of grayscale voltage to the liquid crystal cells in thecenter of the screen are asymmetrical to each other; that is to say, thetiming of application of grayscale voltage to the liquid crystal cellsat the top end of the screen is earlier than the timing of applicationof grayscale voltage to the liquid crystal cells in the center of thescreen, while the timing of application of grayscale voltage to th eliquid crystal cells at the bottom end of the screen is later than thetiming of application of grayscale voltage to the liquid crystal cellsin the center of the screen. As a result, a moving image obtained fromthe countermeasures against moving-image blur that are taken by causingthe backlight to light intermittently in synchronism with verticalsynchronizing signals suffers a double contour which is asymmetrical inthe top and bottom portions of the screen. A degradation of imagequality due to this double contour which occurs asymmetrically in thetop and bottom portions of the screen cannot be substantiallyameliorated even if the lighting start timing of the backlight which isintermittently lit in synchronism with the vertical synchronizing signalis deviated.

[0022] Therefore, the invention provides a liquid crystal display devicewhich can display a high-quality image by reducing a double contourwhich occurs asymmetrically in the top and bottom port ions of itsscreen during the display of a moving image and which cannot besubstantially solved by existing countermeasures against moving-imageblur which cause a back light to light intermittently in synchronismwith vertical synchronizing signals.

[0023] Several means for solving above problem are as follows.

[0024] (1) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is started with a line lying at one end of a screen and with aline Iying at the other end of the screen, and scanning-signal-lineselection started at the one end of the screen is sequentially performedto proceed toward the other end of the screen, whilescanning-signal-line selection started at the other end of the screen issequentially per formed to proceed toward the one end of the screen.Scanning-signal-line selection in an area corresponding to a display area of the liquid crystal panel is completed when the scanning-signal-lineselection started at the one end of the screen and thescanning-signal-line selection started at the other end of the screenrespectively select most mutually adjacent separate scanning signallines. The light source which illuminates the liquid crystal panel islit and extinguished in a predetermined relationship with writing of thedisplay image signal to the screen.

[0025] (2) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is sequentially performed to proceed from one of adjacent scanningsignal lines toward one end of a screen and to proceed from the other ofthe adjacent scanning signal lines toward the other end of the screen,and the light source which illuminates the liquid crystal panel is litand extinguished in a predetermined relationship with writing of thedisplay image signal to the screen.

[0026] (3) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is started with a line lying at one end of a screen and with aline lying at the other end of the screen, and scanning-signal-lineselection started at the one end of the screen is sequentially performedto proceed toward the other end of the screen, whilescanning-signal-line selection started at the other end of the screen issequentially performed to proceed toward the one end of the screen. Thescanning-signal-line selection started at the one end and thescanning-signal-line selection started at the other end are alternatelyperformed, and scanning-signal-line selection in an area correspondingto a display area of the liquid crystal panel is completed when thescanning-signal-line selection started at the one end of the screen andthe scanning-signal-line selection started at the other end of thescreen respectively select most mutually adjacent separate scanningsignal lines. The light source which illumimnates the liquid crystalpanel is lit and extinguished in a predetermined relationship withwriting of the display image signal to the screen.

[0027] (4) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is sequentially performed to proceed from one of adjacent scanningsignal lines toward one end of a screen and to proceed from the other ofthe adjacent scanning signal lines toward the other end of the screen,and scanning-signal-line selection which proceeds from the one of theadjacent scanning signal lines toward the one end of the screen andscanning-signal-lin e selection which proceeds from the other of theadjacent scanning signal lines toward the other end of the screen arealternately performed. The light source which illuminates the liquidcrystal panel is lit and extinguished in a predetermined relationshipwith writing of the display image signal to the screen.

[0028] (5) A liquid crystal display device according to the inventionincludes: a frame memory which stores display data inputted from anexternal device; a unit which arranges the display data stored in theframe memory, in the desired order of scanning-line selection, andapplies a grayscale voltage according to the display data to a liquidcrystal panel; and a control unit which lights and extinguishes anilluminating power source which blinks a light source for illuminatingthe liquid crystal panel, in synchronism with a vertical synchronizingsignal with in a period in which one image is displayed.

[0029] (6) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is started with a line lying at one end of a screen and with aline Iying at the other end of the screen, and scanning-signal-lineselection started at the one end of the screen is sequentially performedto proceed toward the other end of the screen, whilescanning-signal-line selection started at the other end of the screen issequentially performed to proceed toward the one end of the screen. Thelight source which illuminates the liquid crystal panel isintermittently lit.

[0030] (7) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is sequentially performed to proceed from one of adjacent scanningsignal lines toward one end of a screen and to proceed from the other ofthe adjacent scanning signal lines toward the other end of the screen,and the light source which illuminates the liquid crystal panel isintermittently lit.

[0031] (8) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is started with a line lying at one end of a screen and with aline lying at the other end of the screen, and scanning-signal-lineselection started at the one end of the screen is sequentially performedto proceed toward the other end of the screen, whilescanning-signal-line selection started at the other end of the screen issequentially performed to proceed toward the one end of the screen. Thescanning-signal-line selection started at the one end and thescanning-signal-line selection started at the other end are alternatelyperformed, and the light source which illuminates the liquid crystalpanel is intermittently lit.

[0032] (9) A liquid crystal display device according to the inventionincludes: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel.In the liquid crystal display device, selection of the scanning signallines is sequentially performed to proceed from one of adjacent scanningsignal lines toward one end of a screen and to proceed from the other ofthe adjacent scann ing signal lines toward the other end of the screen,and scanning-signal-line selection which proceeds from the one of theadjacent scanning signal lines toward the one end of the screen andscanning-signal-line selection which proceeds from the other of theadjacent scanning signal lines toward the other end of the screen arealternately performed. The light source which illuminates the liquidcrystal panel is intermittently lit.

[0033] (10) In a liquid crystal display device as in (6),scanning-signal-line selection in an area corresponding to a displayarea of the liquid crystal panel is completed when thescanning-signal-line selection started at the one end of the screen andthe scanning-signal-line selection started at the other end of thescreen respectively select most mutually adjacent separate scanningsignal lines.

[0034] (11) A liquid crystal display device as in (6) further includes ascanning driver circuit which supplies scanning signals to the scanningsignal lines and signal driver circuits which supply video signals tovideo signal lines. The signal driver circuits are disposed on the topside and the bottom side of the liquid crystal display device, and thevideo signal lines are connected to either one of the signal drivercircuits disposed on the top side and the bottom side.

[0035] (12) In a liquid crystal display device as in (7), the selectionof the scanning signal lines which proceeds toward the one end of thescreen and the selection of the scanning signal lines which proceedstoward the other end of the screen are performed at approximately thesame time.

[0036] (13) In a liquid crystal display device as in (11), the selectionof the scanning signal lines which proceeds toward the one end of thescreen and the selection of the scanning signal lines which proceedstoward the other end of the screen are performed at approximately thesame time.

[0037] (14) A liquid crystal display device as in (7) further includes ascanning driver circuit which supplies scanning signals to the scanningsignal lines and signal driver circuits which supply video signals tovideo signal lines. The signal driver circuits are disposed on the topside and the bottom side of the liquid crystal display device, and thevideo signal lines are connected to either one of the signal drivercircuits disposed on the top side and the bottom side.

[0038] (15) In a liquid crystal display device as in (7), the selectionof the scanning signal lines sequentially performed to proceed from theone of the adjacent scanning signal lines toward the one end of thescreen and to proceed from the other of the adjacent scann ing signallines toward the other end of the screen are per formed at approximatelythe same time.

[0039] In the liquid crystal display device according to the inventiondescribed in any of (1) to (15), the timing of application of grayscalevoltage to the liquid crystal cells at the top end of the screen withrespect to the timing of application of grayscale voltage to the liquidcrystal cells in the center of the screen and the timing of applicationof grayscale voltage to the liquid crystal cells at the bottom end ofthe screen with respect to the timing of application of grayscalevoltage to the liquid crystal cells in the center of the screen are madecloser to each other or symmetrical to each other on the top and bottomsides of the screen, whereby the setting margin of the lighting starttiming of a back light can be enlarged. Accordingly, it is possible toprovide a liquid crystal display device capable of reducing a doublecontour which occurs asymmetrically on the top and bottom sides of itsscreen during the display of a moving image owing to countermeasuresagainst moving-image blur which are taken by causing the backlight tolight intermittently in synchronism with vertical synchronizing signals.

[0040] Further aspects and advantages of the invention will becomeapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention will become more readily appreciated and understoodfrom the following detailed description of preferred embodiments of theinvention when taken in conjunction with the accompanying drawings, inwhich:

[0042]FIG. 1 is a block diagram of a related art liquid crystal displaydevice

[0043]FIG. 2 shows one example of a block diagram of a liquid crystaldisplay device according to the invention;

[0044]FIG. 3 is a timing chart showing a scanning-line selection methodused in a related art;

[0045]FIG. 4 is a timing chart showing the transmissivities of liquidcrystal cells at the top end of a screen, in the center of the screenand at the bottom end of the screen, as well as a backlight luminanceand a luminance of a liquid crystal panel in the related art;

[0046]FIG. 5 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0047]FIG. 6 is a timing chart showing the transmissivities of liquidcrystal cells at the top end of a screen, in the center of the screenand at the bottom end of the screen, as well as a backlight luminanceand a luminance of a liquid crystal panel in one embodiment of theinvention;

[0048]FIG. 7 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0049]FIG. 8 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0050]FIG. 9 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0051]FIG. 10 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0052]FIG. 11 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0053]FIG. 12 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0054]FIG. 13 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0055]FIG. 14 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0056]FIG. 15 is a driving timing chart showing a scanning-lineselection method used in one embodiment of the invention;

[0057]FIG. 16 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0058]FIG. 17 is a block diagram of another liquid crystal displaydevice according to the invention;

[0059]FIG. 18 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0060]FIG. 19 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0061]FIG. 20 is a timing chart showing a scanning-line selection methodused in one embodiment of the invention;

[0062]FIG. 21 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0063]FIG. 22 is a schematic cross-sectional view aiding in describingan example of the construction of a direct backlight which uses acold-cathode fluorescent lamp as its light source according to oneembodiment of the invention

[0064]FIG. 23 is a timing chart showing the transmissivities of theliquid crystal cells at the top end of the screen, in the center of thescreen and at the bottom end of the screen as well as the backlightluminance and the luminance of the liquid crystal panel in oneembodiment of the invention;

[0065]FIG. 24 is a timing chart showing a scanning-line selection methodaccording to one embodiment of the invention;

[0066]FIG. 25 is a timing chart showing a scanning-line selection methodaccording to one embodiment of the invention;

[0067]FIG. 26 is a timing chart showing a scanning-line selection methodaccording to one embodiment of the invention; and

[0068]FIG. 27 is a timing chart showing a scanning-line selection methodaccording to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0069] Preferred embodiments of the invention will be described belowwith reference to the drawings of the preferred embodiments.

[0070]FIG. 2 is a block diagram of a liquid crystal display device whichrealizes the invention. In FIG. 2, a light source which illuminates aliquid crystal panel and an illuminating device which blinks the lightsource are omitted.

[0071] In FIG. 2, 101 denotes a bus over which to transmit display dataand a synchronizing signal which are inputted from an external device,102 denotes a frame memory control circuit, 103 denotes a frame memorycontroll bus, 104 denotes a frame memory, and 109 denotes a bus overwhich to transmit display data and synchronizing signals which arearranged in the desired order of scanning-line selection by the framememory 104 and the frame memory control circuit 102. 122 denotes atiming control circuit which generates various timing signals for aliquid crystal driver circuit, 111 denotes buses over which to transmitdisplay data and a synchronizing signal which are generated by thetiming control circuit 122, and 112 denotes buses over each of which asynchronizing signal generated by the timing control circuit 122 is tobe transmitted to a corresponding one of scanning driver circuits 114.113 denotes signal driver circuits which generate grayscale voltagesaccording to the display data transmitted over the corresponding ones ofthe buses 111. 114 denotes the scanning driver circuits each of whichsequentially selects lines to which to apply the grayscale voltagegenerated by the corresponding one of the signal driver circuits 113.115 denotes a power source circuit, and 116 denotes a liquid crystalpanel. 117 denotes drain line buses over which to transmit to the liquidcrystal panel 116 the grayscale voltages generated by the signal drivercircuits 113. 118 denotes gate line buses over which to transmitscanning voltages generated by the scanning driver circuits 114 to theliquid crystal panel 116. 119 denotes power source buses over which totransmit power source voltages to the respective scanning drivercircuits 114, and 120 denotes power source buses over which to transmitpower source voltages to the respective signal driver circuits 113.

[0072] In the liquid crystal display device shown in FIG. 2, twoscanning driver circuits 114 and two signal driver circuits 113 areprovided for performing scanning-line selection by two lines at a time.

[0073]FIG. 17 is a block diagram of another liquid crystal displaydevice which is constructed to select one scanning signal line at atime. In FIG. 17, a light source which illuminates a liquid crystalpanel and an illuminating device which blinks the light source areomitted. In FIG. 17, s are the same as those used in FIG. 2. One signaldriver circuit 113 is provided for selecting one scanning signal line ata time. Two scanning driver circuits 114 are provided for alternatelyselecting scanning signal lines in the top and bottom portions of thescreen of the liquid crystal display device.

[0074] Preferred embodiments of the invention will be described belowwith reference to FIGS. 5 to 23.

[0075]FIGS. 5 and 6 are driving timing charts of a liquid crystaldisplay device according to a first embodiment of the invention.

[0076] In FIGS. 5 and 6, 301 denotes a vertical write period (frameperiod), 302 denotes a vertical synchronizing signal 303 denotes ascanning-line selecting signal (gate-line selecting signal), 304 denotesthe transmissivity of liquid crystal cells lying at the top end of thescreen of the liquid crystal display device, 305 denotes thetransmissivity of liquid crystal cells lying in the center of thescreen, and 306 denotes the transmissivity of liquid crystal cells lyingat the bottom end of the screen, 307 denotes a back light luminance. 309denotes the luminance of the liquid crystal panel in the center of thescreen during a period of time in which the transmissivity of the liquidcrystal cells lying in the center of the screen is in its transientstate before reaching its steady state, when display data in the centerof the screen changes from black to white. 311 denotes the luminance ofthe liquid crys tal panel at each of the top and bottom ends of thescreen during a period of time in which the transmissivity of the liquidcrystal cells lying at each of the top and bottom ends of the screen isin its transient state before reaching its steady state, when displaydata at each of the top and bottom ends of the screen changes from blackto white.

[0077] In the first embodiment, selection of scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes is carried out at the timing shown in FIG.5 by using the block diagram of the liquid crystal display device shownin FIG. 2 by the following method: Scanning-line selections arerespectively started with the first line and the N-th line at the sametime, and the scanning-line selection started with the first line isperformed sequentially downwardly of the screen, while the scanning-lineselection started with the N-th line is performed sequentially upwardlyof the screen. The selection of scanning signal lines for one image iscompleted with the selection of both the (N/2)-th line and the (N/2+1)-th line. In this method, the relationship shown in FIG. 6 is achievedamong: the transmissivity 304 of the liquid crystal cells at the top endof the screen, the transmissivity 305 of the liquid crystal cells in thecenter of the screen, the transmissivity 306 of the liquid crystal cellsat the bottom end of the screen, and the backlight luminance 307, all ofwhich are obtained when grayscale voltages corresponding to display dataare applied to the liquid crystal cells of the liquid crystal panel; theluminance 309 of the liquid crystal panel in the center of the screenduring the period of time in which the transmissivity of the liquidcrystal cells lying in the center of the screen is in the transientstate before reaching the steady state, when display data in the centerof the screen changes from black to white; and the luminance 311 of theliquid crystal panel at each of the top and bottom ends of the screenduring the period of time in which the transmissivity of the liquidcrystal cells lying at each of the top and bottom ends of the screen isin the transient state before reach ing the steady state, when displ aydata at each of the top and bottom ends of the screen changes from blackto white.

[0078] When the lighting start timing of a backlight which isintermittently lit in synchronism with the vertical synchronizing signal302 is made the same as that in the related art shown in FIG. 4, thetiming of application of grayscale voltage to the liquid crystal cellsat the top end of the screen with respect to the timing of applicationof grayscale voltage to the liquid crystal cells in the center of thescreen becomes symmetrical to the timing of application of grayscalevoltage to the liquid crystal cells at the bottom end of the screen withrespect to the timing of application of grayscale voltage to the liquidcrystal cells in the center of the screen. Accordingly, the luminance310 shown in FIG. 4 disappears, which is the luminance of the liquidcrystal panel at the bottom end of the screen during the period of timein which the transmissivity of the liquid crystal cells lying at thebottom end of the screen is in the transient state before reaching thesteady state, when display data at the bottom end of the screen changesfrom black to white, and only the luminance 311 is left, which is lowerthan the luminance 310 shown in FIG. 4 and is the luminance of theliquid crystal panel at each of the top and bottom ends of the screenduring the period of time in which the transmissivity of the liquidcrystal cells lying at each of the top and bottom ends of the screen isin the transient state before reaching the steady state, when displaydata at each of the top and bottom ends of the screen changes from blackto white.

[0079] The driving timing chart of FIG. 6 has been described on thebasis of the lighting start timing of the backlight which is the same asthat in the related art shown in FIG. 4. Since the luminance variationsin the top and bottom portions of the screen are symmetrical, even ifthe lighting start timing of the backlight is deviated, the contrast ofa double contour in either of the top and bottom portions of the screendoes not become high during the display of a moving image. Accordingly,by appropriately setting the timing of application of grayscale voltageto the liquid crystal cells at each of the top and bottom ends of thescreen with respect to the timing of application of grayscale voltage tothe liquid crystal cells in the center of the screen, it is possible toreduce a double contour which occurs during the display of a movingimage, at both of the top and bottom ends of the screen.

[0080]FIGS. 18 and 19 are driving timing charts of a liquid crystaldisplay device according to a second embodiment of the invention. Thesecond embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 2. Symbols and numbers shown inFIGS. 18 and 19 are the same as those shown in FIGS. 5 and 6. Thescanning-line selection method shown in FIG. 18 is the same as thatshown in FIG. 5. In FIG. 5, the period of time required to completescanning-line selection is slightly shorter than ½ of a vertical writeperiod (frame period), whereas in FIG. 18, the period of time requiredto complete scanning-line selection is approximately the same as thatadopted in the related art shown in FIG. 3, i.e. , slightly shorter than½ of the vertical write period.

[0081] Specifically, in FIG. 18, the period of time from the start ofselection of an arbitrary scanning line until the start of selection ofthe next scanning line is twice as long as that shown in FIG. 5, but theperiod of time for which the arbitrary scanning line is selected in FIG.18 is the same as that shown in FIG. 5. It goes without saying thatthere is no problem even if the period of time for which an arbitraryscanning line is selected in FIG. 18 is made twice as long as that shownin FIG. 5 and the period of time required to complete scanning-lineselection is made slightly shorter than the vertical write period (frameperiod).

[0082] Referring to FIG. 19, the lighting start timing of the back lightwhich is intermittently lit in synchronism with the verticalsynchronizing signal 302 is made the same as the timing at which afterthe application of grayscale voltage to the liquid crystal cells lyingat each of the top and bottom ends of the screen, the transmissivity ofeach of the liquid crystal cells reaches an approximately steady stateduring the period of time in which the transmissivity of each of theliquid crystal cells is in the transient state before reaching thesteady state.

[0083] In this case, the luminance 311 is the luminance of the liquidcrystal panel during the period of time in which the transmissivity ofthe liquid crystal cells lying at each of the top and bottom ends of thescreen is in the transient state before reaching the steady state, whendisplay data at each of the top and bottom ends of the screen changesfrom black to white, and the luminance 309 is the luminance of theliquid crystal panel during the period of time in which thetransmissivity of the liquid crystal cells lying in the center of thescreen is in the transient state before reaching the steady state, whendisplay data in the center of the screen changes from black to white.

[0084] In the second embodiment, since the luminance of the liquidcrystal panel at each of the top and bottom ends of the screen graduallyincreases when display data changes from black to white, a doublecontour does not occur even if a moving image is displayed. In thecenter of the screen, when display data changes from black to white, thebacklight is lit while the transmissivity of the liquid crystal cells inthe center of the screen is in the steady state after the emission oflight of extremely low luminance (low contrast). Although an emission ofhigh luminance occurs and therefore, an extremely thin double contourappears, the image quality is improved in the entire screen. Inaddition, in the second embodiment, the period of time from the start ofselection of an arbitrary scanning line until the start of selection ofthe next scanning line is made twice as long as that shown in FIG. 5 interms of the response time of a variation in the transmissivity of theliquid crystal cells to the application of grayscale voltage and theluminance response time of the backlight. However, it goes withoutsaying that in the case where the response time of avariation in thetransmissivity of the liquid crystal cells to the application ofgrayscale voltage and the luminance response time of the back light aredifferent from those shown in FIG. 19, the image quality can be improvedby appropriately setting the period of time from the start of selectionof an arbitrary scanning line until the start of selection of the nextscanning line within the range of from once to twice as long as thatshown in FIG. 5.

[0085]FIGS. 7 and 8 are driving timing charts of a liquid crystaldisplay device according to a third embodiment of the invention. Thethird embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 2. The s shown in FIGS. 7 and 8 arethe same as those shown in FIGS. 5 and 6.

[0086] In the third embodiment, selection of scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes is carried out at the timing shown in FIG.7 by using the block diagram of the liquid crystal display device shownin FIG. 2 by the following method: Scanning-line selections arerespectively started with the (N/2)-th line and the (N/2+1)-th line atthe same time, and the scanning-line selection started with the (N/2)-thline is performed sequentially upwardly of the screen, while thescanning-line selection started with the (N/2+1)-th line is performedsequentially downwardly of the screen. The selection of scanning signallines for one image is completed with the selection of both the firstline and the N-th line. In this method, grayscale voltages correspondingto display data are applied to the respective liquid crystal cell S.

[0087] Referring to FIG. 8, the lighting start timing of the back lightwhich is intermittently lit in synchronism with the verticalsynchronizing signal 302 is made the same as the timing of applicationof grayscale voltage to the liquid crystal cell s in the center of thescreen.

[0088] In this case, the luminance 309 is the luminance of the liquidcrystal panel during the period of time in which the transmissivity ofthe liquid crystal cells lying in the center of the screen is in thetransient state before reaching the steady state, when display data inthe center of the screen changes from black to white, and the luminance311 is the luminance of the liquid crystal panel during the period oftime in which the transmissivity of the liquid crystal cells lying ateach of the top and bottom ends of the screen is in the transient statebefore reaching the steady state, when display data at each of the topand bottom ends of the screen changes from black to white.

[0089] In FIG. 8, similarly to FIG. 6, the luminance 310 shown in FIG. 4disappears, which is the luminance of the liquid crystal panel at thebottom end of the screen during the period of time in which thetransmissivity of the liquid crystal cells lying at the bottom end ofthe screen is in the transient state before reaching the steady state,and only the luminance 311 is left, which is lower (lower in contrast)than the luminance 310 shown in FIG. 4 and is the luminance of theliquid crystal panel at each of the top and bottom ends of the screenduring the period of time in which the transmissivity of the liquidcrystal cells at each of the top and bottom ends of the screen is in thetransient state before reaching the steady state.

[0090] In FIG. 8, the lighting start timing of the back light which isintermittently lit in synchronism with the vertical synchronizing signal302 is made the same as the timing of application of grayscale voltageto the liquid crystal cells in the center of the screen. Accordingly,the gradual increase of the luminance 309 shown in FIG. 8 is slightlysluggish compared to the variation in the luminance 309, shown in FIG.6, of the liquid crystal panel in the center of the screen during theperiod of time in which the transmissivity of the liquid crystal cellslying in the center of the screen is in the transient state beforereaching the steady state.

[0091] However, in FIG. 8 as well, the luminance 311 of the liquidcrystal panel at each of the top and bottom ends of the screen duringthe period of time in which the transmissivity of the liquid crystalcells lying at each of the top and bottom ends of the screen is in thetransient state before reaching the steady state is similar to theluminance 311 shown in FIG. 6, and the contrast of a double contour ineither of the top and bottom portions of the screen does not become highduring the display of a moving image. Accordingly, by appropriatelysetting the timing of application of grayscale voltage to the liquidcrystal cells at each of the top and bottom ends of the screen withrespect to the timing of application of grayscale voltage to the liquidcrystal cells in the center of the screen, it is possible to reduce adouble contour which occurs during the display of a moving image, atboth of the top and bottom ends of the screen.

[0092]FIGS. 20 and 21 are driving timing charts of a liquid crystaldisplay device according to a fourth embodiment of the invention. Thefourth embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 2. The s shown in FIGS. 20 and 21are the same as those shown in FIGS. 5 and 6.

[0093] The scanning-line selection method shown in FIG. 20 is the sameas that shown in FIG. 7. In FIG. 7, the period of time required tocomplete scanning-line selection is slightly shorter than ½ of thevertical write period (frame period), whereas in FIG. 20, the period oftime required to complete scanning-line selection is approximately thesame as that adopted in the related art shown in FIG. 3, i.e., slightlyshorter than the vertical write period.

[0094] Specifically, in FIG. 20, the period of time from the start ofselection of an arbitrary scanning line until the start of selection ofthe next scanning line is twice as long as that shown in FIG. 7, but theperiod of time for which the arbitrary scanning line is selected in FIG.20 is the same as that shown in FIG. 7. It goes without saying thatthere is no problem even if the period of time for which an arbitraryscanning line is selected in FIG. 20 is made twice as long as that shownin FIG. 7 and the period of time required to complete scanning-lineselection is made slightly shorter than the vertical write period (frameperiod).

[0095] Referring to FIG. 21, the lighting start timing of the back lightwhich is intermittently lit in synchronism with the verticalsynchronizing signal 302 is made the same as the timing at which thetransmissivity of the liquid crystal cells changes from the transientstate to the steady state after the application of grayscale voltage tothe liquid crystal cells lying in the center of the screen.

[0096] In this case, the luminance 309 is the luminance of the liquidcrystal panel during the period of time in which the transmissivity ofthe liquid crystal cells lying in the center of the screen is in thetransient state before reaching the steady state, when display data inthe center of the screen changes from black to white, and the luminance311 is the luminance of the liquid crystal panel during the period oftime in which the transmissivity of the liquid crystal cells lying ateach of the top and bottom ends of the screen is in the transient statebefore reaching the steady state, when display data at each of the topand bottom ends of the screen changes from black to white.

[0097] In the fourth embodiment, since the luminance of the liquidcrystal panel in the center of the screen gradually increases whendisplay data changes from black to white, a double contour does notoccur even if a moving image is displayed. At each of the top and bottomends of the screen, when display data changes from black to white, thebacklight is lit while the transmissivity of the liquid crystal cells ateach of the top and bottom ends of the screen is in the steady stateafter the emission of light of extremely low luminance (low contrast).Although an emission of high luminance occurs and therefore, anextremely thin double contour appears, the image quality is improved inthe entire screen.

[0098] In the fourth embodiment, the period of time from the start ofselection of an arbitrary scanning line until the start of selection ofthe next scanning line is made twice as long as that shown in FIG. 7 interms of the response time of a variation in the transmissivity of theliquid crystal cells to the application of grayscale voltage and theluminance response time of the backlight. However, it goes withoutsaying that in the case where the response time of a variation in thetransmissivity of the liquid crystal cells to the application ofgrayscale voltage and the luminance response time of the backlight aredifferent from those shown in FIG. 21, the image quality can be improvedby appropriately setting the period of time from the start of selectionof an arbitrary scanning line until the start of selection of the nextscanning line with in the range of from once to twice as long as thatshown in FIG. 7.

[0099]FIGS. 9 and 10 are driving timing charts of a liquid crystaldisplay device according to a fifth embodiment of the invention. Thefifth embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 17. The s shown in FIGS. 9 and 10are the same as those shown in FIGS. 5 and 6.

[0100] Referring to FIG. 9, from among the scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes, the N-th line is selected after the firstline is se lected, then the second line is selected after the N-th lineis selected, then the (N−1)-th line is selected after the second line isselected, and subsequently, the selections of the remaining scanninglines are similarly sequentially performed. When the (N2+1)-th line hasbeen selected after the (N/2)-th line has been selected, the selectionof scanning signal lines for one image is completed.

[0101] The scanning-line selection is performed at the timing shown inFIG. 9, and the lighting start timing of the backlight which isintermittently lit in synchronism with the vertical synchronizing signal302 shown in FIG. 10 is made the same as the timing at which after theapplication of grayscale voltage to the liquid crystal cells lying ateach of the top and bottom ends of the screen, the transmissivity ofeach of the liquid crystal cells reaches an approximately steady stateduring the period of time in which the transmissivity of each of theliquid crystal cells is in the transient state before reaching thesteady state.

[0102] In FIG. 9, the timing of application of grayscale voltage to theliquid crystal cells at the top end of the screen and the timing ofapplication of grayscale voltage to the liquid crystal cells at thebottom end of the screen are deviated from each other by the period oftime from the start of selection of an arbitrary scanning line until thestart of selection of the next scanning line. In a liquid crystal panelhaving 1,024 (in length)×768 (in width) effective pixels, the totalnumber of lines including the number of lines lying in its non-displ ayarea is 800 to 808, although there is a difference between the numbersof lines of in dividual systems. Therefore, the selection time per lineis approximately 21 μS in the case of a screen display frequency of 60Hz (16.7 mS), and is not greater than 1/100 of the response time of aliquid crystal having a normal response time. Accordingly, such a periodof time is a negligible time difference.

[0103] Accordingly, the respective driving timing charts of FIGS. 9 and10 are similar to those of FIGS. 18 and 19, whereby it is possible toobtain an image-quality improvement effect similar to that achieved inthe second embodiment described above with reference to FIGS. 18 and 19.

[0104]FIGS. 11 and 12 are driving timing charts of a liquid crystaldisplay device according to a sixth embodiment of the invention. Thesixth embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 17. The s shown in FIGS. 11 and 12are the same as those shown in FIGS. 5 and 6.

[0105] Referring to FIG. 11, from among the scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes, the first line is selected after the N-thline is selected, then the (N−1)-th line is selected after the firstline is selected, then the second line is selected after the (N−1)-thline is selected, and subsequently, the selections of the remainingscanning lines are similarly sequentially performed. When the (N/2)-thline is selected after the (N/2+1)-th line has been selected, theselection of scanning signal lines for one image is completed.

[0106] The scanning-line selection is performed at the timing shown inFIG. 11, and the lighting start timing of the back light which isintermittently lit in synchronism with the vertical synchronizing signal302 shown in FIG. 12 is made the same as the timing at which after theapplication of grayscale voltage to the liquid crystal cells lying ateach of the top and bottom ends of the screen, the transmissivity ofeach of the liquid crystal cells reaches an approximately steady stateduring the period of time in which the transmissivity of each of theliquid crystal cells is in the transient state before reaching thesteady state.

[0107] The difference between FIGS. 9 and 11 is that in FIG. 9,scanning-line selection is started at the top end of the screen, whereasin FIG. 11, scanning-line selection is started at the bottom end of thescreen. As described above, in a liquid crystal panel having 1,024 (inlength)×768 (in width) effective pixels, the time difference between thestart of selection of an arbitrary scanning line and the start ofselection of the next scanning line is approximately 21

S, and is not greater than 1/100 of the response time of a liquidcrystal having a normal response time. Accordingly, such a period oftime is a negligible time difference.

[0108] Accordingly, the respective driving timing charts of FIGS. 11 and12 are similar to those of FIGS. 9 and 10 and hence those of FIGS. 18and 19, whereby it is possible to obtain an image-quality improvementeffect similar to that achieved in the second embodiment described abovewith reference to FIGS. 18 and 19.

[0109]FIGS. 13 and 14 are driving timing charts of a liquid crystaldisplay device according to a seventh embodiment of the invention. Theseventh embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 17. The s shown in FIGS. 13 and 14are the same as those shown in FIGS. 5 and 6.

[0110] Referring to FIG. 13, from among the scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes, the (N/2+1)-th line is selected after the(N/2)-th line is selected, then the (N/2−1)-th line is selected afterthe (N/2+1)-th line is selected, then the (N/2+2)-th line is selectedafter the (N/2−1)-th line is selected, and subsequently, the selectionsof the remaining scanning lines are similarly sequentially performed.When the N-th line is selected after the first line has been selected,the selection of scanning signal lines for one image is completed.

[0111] The scanning-line selection is performed at the timing shown inFIG. 13, and the lighting start timing of the backlight which isintermittently lit in synchronism with the vertical synchronizing signal302 shown in FIG. 14 is made the same as the timing at which after theapplication of grayscale voltage to the liquid crystal cells lying inthe center of the screen, the transmissivity of the liquid crystal cellschanges from the transient state to the steady state.

[0112] The difference between the timing of application of grayscalevoltage to the liquid crystal cels along the (N/2+1)-th line in thecenter of the screen and the timing of application of grayscale voltageto the liquid crystal cell along the (N/2)-th line in the center of thescreen, and the difference between the timing of application ofgrayscale voltage to liquid crystal cells at the bottom end of thescreen and the timing of application of grayscale voltage to liquidcrystal cells at the top end of the screen, are each equivalent to theperiod of time from the start of selection of an arbitrary scanning lineuntil the start of selection of the next scanning line. However, asdescribed above, in a liquid crystal panel having 1,024 (in length)×768(in width) effective pixels, the time difference between the start ofselection of an arbitrary scanning line and the start of selection ofthe next scanning line is approximately 21 z,900 S, and is not greaterthan 1/100 of the response time of a liquid crystal having a normalresponse time. Accordingly, such a period of time is a negligible timedifference.

[0113] Accordingly, according to the respective driving timing charts ofFIGS. 13 and 14, it is possible to obtain an image-quality improvementeffect similar to that achieved in the fourth embodiment described abovewith reference to FIGS. 20 and 21.

[0114]FIGS. 15 and 16 are driving timing charts of a liquid crystaldisplay device according to an eighth embodiment of the invention. Theeighth embodiment is realized by using the block diagram of the liquidcrystal display device shown in FIG. 17. The s shown in FIGS. 15 and 16are the same as those shown in FIGS. 5 and 6.

[0115] Referring to FIG. 15, from among the scanning signal lines of aliquid crystal panel having N number of scanning signal lines and Nlines of scanning electrodes, the (N/2)-th line is selected after the(N/2+1)-th line is selected, then the (N/2+1)-th line is selected afterthe (N/2)-th line is selected, then the (N/2−1)-th line is selectedafter the (N/2+2)-th line is selected, and subsequently, the selectionsof the remaining scanning lines are similarly sequentially performed.When the first line is selected after the N-th line has been selected,the selection of scanning signal lines for one image is completed.

[0116] The scanning-line selection is performed at the timing shown inFIG. 15, and the lighting start timing of the back light which isintermittently lit in synchronism with the vertical synchronizing signal302 shown in FIG. 16 is made the same as the timing at which after theapplication of grayscale voltage to the liquid crystal cells lying inthe center of the screen, the transmissivity of the liquid crystal cellschanges from the transient state to the steady state.

[0117] The difference between the timing of application of grayscalevoltage to the liquid crystal cells along the (N/2+1)-th line in thecenter of the screen and the timing of application of grayscale voltageto the liquid crystal cell along the (N/2)-th line in the center of thescreen, and the difference between the timing of application ofgrayscale voltage to liquid crystal cells at the bottom end of thescreen and the timing of application of grayscale voltage to liquidcrystal cells at the top end of the screen, are each equivalent to theperiod of time from the start of selection of an arbitrary scanning lineuntil the start of selection of the next scanning line. However, asdescribed above, in a liquid crystal panel having 1,024 (in length)×768(in width) effective pixels, the time difference between the start ofselection of an arbitrary scanning line and the start of selection ofthe next scanning line is approximately 21 μS, and is not greater than1/100 of the response time of a liquid crystal having a normal responsetime. Accordingly, such a period of time is a negligible timedifference.

[0118] Accordingly, according to the respective driving timing charts ofFIGS. 15 and 16, it is possible to obtain an image-quality improvementeffect similar to that achieved in the fourth embodiment described abovewith reference to FIGS. 20 and 21.

[0119]FIG. 22 is a schematic cross-sectional view showing a ninthembodiment of the invention and aiding in describing an example of theconstruction of a direct backlight which uses a cold-cathode fluorescentlamp as its light source. Referring to FIG. 22, in the direct backlight,a reflecting sheet 7 for efficiently using light of a plurality ofcold-cathode fluorescent lamps 4 is provided at the bottom of a frame 1.A diffusion sheet 2 is provided on a liquid-crystal-panel side (notshown) of the direct backlight.

[0120] Formed on the bottom surface of the diffusing sheet 2 arelight-shielding dots 3 for adjusting the luminance of light of thecorresponding cold-cathode fluorescent lamps 4 disposed directly belowthe respective light-shielding dots 3. Related arts of this kind ofdirect backlight have been disclosed in, for example, Japanese PatentLaid-Open Nos. 242219/1999 and 84377/1999.

[0121] In the direct back light shown in FIG. 22, select ion of scanningsignal lines of a liquid crystal panel having N number of scanningsignal lines and N lines of scanning electrodes is carried out at thetiming shown in FIG. 5 by using the block diagram of the liquid crystaldisplay device shown in FIG. 2 by the following method: Scanning-lineselections are respectively started with the first line and the N-thline at the same time, and the scanning-line selection started with thefirst line is performed sequentially downwardly of the screen, while thescanning-line selection started with the N-th line is performedsequentially upwardly of the screen. The selection of scanning signallines for one image is completed with the selection of both the (N/2)-thline and the (N/2+1)-th line.

[0122]FIG. 23 is a driving timing chart of a liquid crystal displaydevice according to the ninth embodiment of the invention.

[0123] The lighting start timing of the back light which isintermittently lit in synchronism with the vertical synchronizing signal302 shown in FIG. 23 is made the same as the timing of a backlightluminance 320 as to the backlight lamp 4 which illuminates liquidcrystal cells near the center of the screen, and as the timing of abacklight luminance 321 as to the backlight lamps 4 which illuminateliquid crystal cells in the top and bottom portions of the screen.

[0124] When scanning-line selection is performed at the above-describedtiming while the intermittent lighting of the backlight is beingperformed, the luminance 309 becomes the luminance of the liquid crystalpanel in the center of the screen during the period of time in which thetransmissivity of liquid crystal cells lying in the center of the screenis in the transient state before reaching the steady state, when displaydata in the center of the screen changes from black to white, while theluminance 311 becomes the luminance of the liquid crystal panel at eachof the top and bottom ends of the screen when display data at each ofthe top and bottom ends of the screen changes from black to white.

[0125] In the center of the screen, when the display data changes fromblack to white, the waveform of the liquid crystal panel during theperiod of time in which the transmissivity of the liquid crystal cellsis in the transient state before reaching the steady state is such thatthe luminance of the liquid crystal panel gradually increases as shownat 309, and in addition, a variation in the luminance of the liquidcrystal panel is faster than the response of a variation in thetransmissivity of the liquid crystal cells to the application ofgrayscale voltage to the liquid crystal cells. Accordingly, the imagequality of the liquid crystal display device is improved.

[0126] At each of the top and bottom ends of the screen, when thedisplay data changes from black to white, the backlight is lit while thetransmissivity of the liquid crystal cells at each of the top and bottomends of the screen is in the steady state after the emission of light ofextremely low luminance (low contrast) . Accordingly, an emission ofhigh luminance occurs and therefore, a double contour can be madeextremely thin, the image quality is improved in the entire screen.

[0127]FIG. 24 shows an example in which scanning signal lines arealternately scanned by two lines at a time. The scanning signal linesare alternately scanned in such a manner that the top first and secondlines are scanned, then the bottom N-th and (N−1)-th lines are scanned,then the top third and fourth lines are scanned, then the bottom(N−2)-th and (N−3)-th line are scanned, and so on. By alternatelyscanning the scanning signal lines, it is possible to average and thin adouble contour at the top and bottom portions of the screen, whereby theimage quality of the liquid crystal display device is improved. The unitof scanning is not limited to two lines, and may also be two or fourlines. In VGA, SVGA and XGA, scanning may be performed in units of threeor four lines. In SXGA, scanning may be performed in units of fourlines. Incidentally, in the fourth embodiment, the terms VGA, SVGA, XGAand SXGA are used to represent the numbers of scanning lines defined bythe respective terms, and the invention can be similarly applied topanels having different horizontal pixel sizes. For instance, a widetype such as WXGA (Wide-XGA), which has the same number of pixels in thelongitudinal direction as XGA and more pixels in the horizontaldirection than XGA, can be handled as XGA.

[0128]FIG. 25 shows an example in which the starting point of scanningdiffers from that of the example shown in FIG. 24. Both examples differin that scanning is started at the top side of the screen in the exampleshown in FIG. 24, whereas in the example shown in FIG. 25, scanning isstarted at the bottom side of the screen. Even with the method shown inFIG. 25, it is possible to obtain an effect equivalent to that of themethod shown in FIG. 24.

[0129]FIG. 26 shows an example in which the scanning shown in FIG. 24 isperformed to proceed from the center toward the top and bottom of thescreen. As shown in FIG. 26, the (N/2)-th and (N/2−1)-th lines arescanned, then the bottom (N/2+1)-th and (N/2+2)-th lines are scanned,then the top (N/2−2)-th and (N/2−3)-th line are scanned, and then thebottom (N/2+3)-th and (N/2+4)-th lines are scanned. Even in this method,it is possible to obtain an image-quality improvement effect similar tothat achieved in the example shown in FIG. 24.

[0130]FIG. 27 shows an example in which the scanning shown in FIG. 26 isstarted at the bottom of the screen. Even in this method, it is possibleto obtain an image-quality improvement effect similar to that achievedin the example shown in FIG. 24.

[0131] As is apparent from the foregoing description, according to theinvention, it i s possible to symmetrize a double contour whichasymmetrically occurs in the top and bottom portions of a screen duringthe display of a moving image. In addition, it is possible to reduce thestrength of the double contour. Accordingly, it is possible to provide aliquid crystal display device capable of restraining the degradation ofimage quality and displaying a high-quality moving image.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal panel having a plurality of drain signal lines and aplurality of scanning signal lines on at least one of a pair ofsubstrates disposed in opposition to each other, and a liquid crystallayer formed between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel,wherein selection of the scanning signal lines being started with a linelying at one end of a screen and with a line lying at the other end ofthe screen, scanning-signal-line selection started at the one end of thescreen being sequentially performed to proceed toward the other end ofthe screen, scanning-signal-line selection started at the other end ofthe screen being sequentially performed to proceed toward the one end ofthe screen scanning-signal-line selection in an area corresponding to adisplay area of the liquid crystal display panel being completed whenthe scanning-signal-line selection started at the one end of the screenand the scanning-signal-line selection started at the other end of thescreen respectively select most mutually adjacent separate scanningsignal lines, the light source which illuminates the liquid crystalpanel being lit and extinguished in a predetermined relationship withwriting of the display image signal to the screen.
 2. A liquid crystaldisplay device comprising: a liquid crystal panel having a plurality ofdrain signal lines and a plurality of scanning signal lines on at leastone of a pair of substrates disposed in opposition to each other, and aliquid crystal layer clamped between the pair of substrates; a displaycontrol unit which applies a voltage according to a display image signalon the basis of a display image signal and a timing signal which areexternally inputted; and a light source which illuminates the liquidcrystal panel, where in selection of the scanning signal lines beingsequentially performed to proceed from one of adjacent scanning signallines toward one end of a screen and to proceed from the other of theadjacent scanning signal lines toward the other end of the screen, thelight source which illuminates the liquid crystal panel being lit andextinguished in a predetermined relationship with writing of the displayimage signal to the screen.
 3. A liquid crystal display devicecomprising: a liquid crystal panel having a plurality of drain signallines and a plurality of scanning signal lines on at least one of a pairof substrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel,wherein selection of the scanning signal lines being started with a linelying at one end of a screen and with a line lying at the other end ofthe screen, scanning-signal-line selection started at the one end of thescreen being sequentially performed to proceed toward the other end ofthe screen, scann ing-signal-line selection started at the other end ofthe screen being sequentially performed to proceed toward the one end ofthe screen, the scanning-signal-line selection started at the one endand the scanning-signal-line selection started at the other end beingalternately performed, scanning-signal-line selection in an areacorresponding to a display area of the liquid crystal display panelbeing completed when the scanning-signal-line selection started at theone end of the screen and the scanning-signal-line selection started atthe other end of the screen respectively select most mutually adjacentseparate scanning signal lines, the light source which illuminates theliquid crystal panel being lit and extinguished in a predeterminedrelationship with writing of the display image signal to the screen. 4.A liquid crystal display device comprising: a liquid crystal panelhaving a plurality of drain signal lines and a plurality of scanningsignal lines on at least one of a pair of substrates disposed inopposition to each other, and a liquid crystal layer clamped between thepair of substrates; a display control unit which applies a voltageaccording to a display image signal on the basis of a display imagesignal and a timing signal which are externally inputted; and a lightsource which illuminates the liquid crystal panel, wherein selection ofthe scanning signal lines being sequentially performed to proceed fromone of adjacent scanning signal lines toward one end of a screen and toproceed from the other of the adjacent scanning signal lines toward theother end of the screen, scanning-signal-line selection which proceedsfrom the one of the adiacent scanning signal lines toward the one end ofthe screen and scanning-signal-line selection which proceeds from theother of the adjacent scanning signal lines toward the other end of thescreen being alternately performed, the light source which illuminatesthe liquid crystal panel being lit and extinguished in a predeterminedrelationship with writing of the display image signal to the screen. 5.A liquid crystal display device comprising: a liquid crystal panelhaving a plurality of drain signal lines and a plurality of scanningsignal lines on at least one of a pair of substrates disposed inopposition to each other, and a liquid crystal layer clamped between thepair of substrates; a display control unit which applies a voltageaccording to a display image signal on the basis of a display imagesignal and a timing signal which are externally inputted; and a lightsource which illuminates the liquid crystal panel, wherein selection ofthe scanning signal lin es being started with a line lying at one end ofa screen and with a line lying at the other end of the screen,scanning-signal-line selection started at the one end of the screenbeing sequentially performed to proceed toward the other end of thescreen, scanning-signal-line selection started at the other end of thescreen being sequentially performed to proceed toward the one end of thescreen, the light source which illuminates the liquid crystal panelbeing intermittently lit.
 6. A liquid crystal display device comprising:a liquid crystal panel having a plurality of drain signal lines and aplurality of scanning signal lines on at least one of a pair ofsubstrates disposed in opposition to each other, and a liquid crystallayer clamped between the pair of substrates; a display control unitwhich applies a voltage according to a display image signal on the basisof a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel,wherein selection of the scanning signal lines being sequentiallyperformed to proceed from one of adjacent scanning signal lines towardone end of a screen and to proceed from the other of the adjacentscanning signal lines toward the other end of the screen, the lightsource which illuminates the liquid crystal panel being intermittentlylit.
 7. A liquid crystal display device comprising: a liquid crystalpanel having a plurality of drain signal lines and a plurality ofscanning signal lines on at least one of a pair of substrates disposedin opposition to each other, and a liquid crystal layer clamped betweenthe pair of substrates; a display control unit which applies a voltageaccording to a display image signal on the basis of a display imagesignal and a timing signal which are externally inputted; and a lightsource which illuminates the liquid crystal panel, wherein selection ofthe scanning signal lines being started with a line lying at one end ofa screen and with a line lying at the other end of the screen,scanning-signal-line selection started at the one end of the screenbeing sequentially performed to proceed toward the other end of thescreen, scanning-signal-line selection started at the other end of thescreen being sequentially performed to proceed toward the one end of thescreen, the scanning-signal-line selection started at the one end andthe scanning-signal-line selection started at the other end beingalternately performed, the light source which illuminates the liquidcrystal panel being intermittently lit.
 8. A liquid crystal displaydevice comprising: a liquid crystal panel having a plurality of drainsignal lines and a plurality of scanning signal lines on at least one ofa pair of substrates disposed in opposition to each other, and a liquidcrystal layer clamped between the pair of substrates; a display controlunit which applies a voltage according to a display image signal on thebasis of a display image signal and a timing signal which are externallyinputted; and a light source which illuminates the liquid crystal panel,wherein selection of the scanning signal lines being sequentiallyperformed to proceed from one of adjacent scanning signal lines towardone end of a screen and to proceed from the other of the adjacentscanning signal lines toward the other end of the screen,scanning-signal-lines selection which proceeds from the one of theadjacent scanning signal lines toward the one end of the screen andscanning-signal-line selection which proceeds from the other of theadjacent scanning signal lines toward the other end of the screen beingalternately performed, the light source which illuminates the liquidcrystal panel being intermittently lit.
 9. A liquid crystal displaydevice according to claim 5, wherein scanning-signal-line selection inan area corresponding to a display area of the liquid crystal panel iscompleted when the scanning-signal-line selection started at the one endof the screen and the scanning-signal-line selection started at theother end of the screen respectively select most mutually adjacentseparate scanning signal lines.
 10. A liquid crystal display deviceaccording to claim 5, further comprising a scanning driver circuit whichsupplies scanning signals to the scanning signal lines and signal drivercircuits which supply video signals to video signal lines, the signaldriver circuits being disposed on the top side and the bottom side ofthe liquid crystal display device, the video signal lines beingconnected to either one of the signal driver circuits disposed on thetopside and the bottom side.
 11. A liquid crystal display deviceaccording to claim 6, wherein the selection of the scanning signal lineswhich proceeds toward the one end of the screen and the selection of thescanning signal lines which proceeds toward the other end of the screenare performed at approximately the same time.
 12. A liquid crystaldisplay device according to claim 10, where in the selection of thescanning signal lines which proceeds toward the one end of the screenand the selection of the scanning signal lines which proceeds toward theother end of the screen are performed at approximately the same time.13. A liquid crystal display device according to claim 6, furthercomprising a scanning driver circuit which supplies scanning signals tothe scanning signal lines and signal driver circuits which supply videosignals to video signal lines, the signal driver circuits being disposedon the top side and the bottom side of the liquid crystal displaydevice, the video signal lines being connected to either one of thesignal driver circuits disposed on the topside and the bottom side. 14.A liquid crystal display device according to claim 6, wherein theselection of the scanning signal lines sequentially performed to proceedfrom the one of the adjacent scanning signal lines toward the one end ofthe screen and to proceed from the other of the adjacent scanning signallines toward the other end of the screen are performed at approximatelythe same time.